Barracuda Active DDoS Prevention is a service that protects you against volumetric DDoS attacks. Combined with the Application DDoS protection features of the Barracuda Web Application Firewall, Barracuda Active DDoS Prevention gives you comprehensive protection from all types of DDoS attacks. In a Distributed Denial of Service (DDoS) attack, the attacker uses many different sources for the fake traffic - typically tens or hundreds of thousands. This makes it difficult to stop the attack by identifying and blocking a list of sources. A DDoS attack can be likened to sending a crowd of people to a retail store, who stand and block the entryway, preventing legitimate customers from entering.